Social: Why Our Brains Are Wired to Connect (8 page)

In trying to understand the links between social and physical pain, we have focused primarily on a brain region called the
dorsal anterior cingulate cortex
, or dACC (
dorsal
means toward the top of the brain, and
anterior
means toward the front of the brain), and
to a lesser extent on the
anterior insula
, or AI (see
Figure 3.2
).
The
cingulate cortex
is a long brain structure that stretches from the back to the front of the brain, hugging the
corpus callosum
on the
midline
, or middle, of the brain.
The word
cingulate
comes from the Latin word
cingere
, which means belt or girdle, and the cingulate looks like a belt for the corpus callosum.
To get a better sense of these regions, try searching for them with Google Images, and scan through the images that come up.
These pictures can help you visualize where the brain regions are in relation to one another, beyond what I can show here in a single figure.
There are literally countless pictures of every brain region available on the Internet.

Figure 3.2 The Dorsal Anterior Cingulate Cortex (dACC), the Rostral Anterior Cingulate Cortex (rACC), and the Anterior Insula (AI)

There are four reasons why an investigation
of the links between social and physical pain would lead to the ACC (anterior cingulate cortex) in general and to the dACC in particular.
First, the ACC is one of the neural adaptations that distinguishes mammals from our reptilian ancestors.
We have cingulates and reptiles do not.
It makes sense to expect that new psychological processes first emerging in mammals, like attachment and social pain, might be linked to new mammalian brain structures like the ACC.
Second,
the ACC has the highest density of opioid receptors
of any region in the brain, so it makes sense that physical and social pain may well be linked to this specific region.
Third, it has been shown that the dACC plays an instrumental role in the experience of physical pain.
Last, the dACC has been linked to mother-infant attachment behavior in various nonhuman mammals.
Let’s take these last two roles of the dACC in turn.

Over the last two decades, a great deal has been learned about the neuroanatomy of pain processes in the human brain.
There are separate sets of cortical brain regions involved in the sensory and distressing aspects of pain.
The
sensory aspects of pain
tell us where
in the body the pain is coming from and how intense the stimulation is.
Two regions residing in the back half of the brain, the
somatosensory cortex
and the
posterior insula
, track the sensory aspects of pain.
The somatosensory cortex maps the different parts of our body, with distinct regions responding to pain in your legs, hands, or face.
(The same regions also respond to nonpainful touch to the corresponding areas.) The posterior insula keeps track of pain sensations in our internal organs and viscera (that is, our gut feelings).
In contrast, the dACC and the anterior insula, located in the front half of the brain, respond to the
distressing aspects of pain
—the feeling that makes pain something we really don’t like.

Because pain feels like a single feeling while we are experiencing it, it’s counterintuitive to imagine that there really are separable components to our experience of pain.
This is a general trick of how the brain works.
There are commonly multiple distinct components to any experience, but by the time it reaches consciousness, it is integrated into something that feels like one coherent event.

Imagine watching a person cross the street.
It feels like a single fluid perception.
In fact,
many different brain regions are working together
to orchestrate this experience.
Some regions of the visual cortex code for all the lines and edges you see (vertical, horizontal, and diagonal lines).
Another region keeps track of the color elements.
Yet another takes in the motion from the scene you are
watching.
And each of these components can be knocked out while still leaving the others intact.
We know this because of rare neuro-psychological case studies that involve damage to a circumscribed brain region.
For instance,
there are patients with damage to motion perception centers
who experience the world as a series of still photos, full of color and detail but with no intervening motion.

Similarly, neuropsychological cases have helped us figure out the distinct contributions of the dACC and the somatosensory cortex when it comes to pain.
In the 1950s, neurosurgeons began performing a procedure called a
cingulotomy
on some patients with intractable pain.
In this surgery, part of the dACC is removed or disconnected from surrounding areas.
This surgery has been successfully used
to treat depression and anxiety.
But its greatest utility has come for individuals with chronic pain conditions that were not amenable to other kinds of treatment.
The most striking thing about cingulotomies is the experience that chronic pain sufferers have postoperatively.
They report that they still feel pain
, and they can point to where it is on their bodies and indicate how intense it is.
But also they report that the pain now is “not distressing,” “not particularly bothersome,” and “doesn’t worry me anymore.”
For anyone with an intact dACC, it’s nearly inconceivable that an individual could feel pain without experiencing the pain as distressing or bothersome, but that seems to be exactly what a cingulotomy allows.
If removing or disconnecting a dACC selectively removes the distressing component of pain, this outcome implies that an intact dACC is central to this distress.

In another case, a stroke victim with selective damage to the somatosensory cortex on the right side of his brain (which keeps track of the left side of one’s body) experienced pain-related changes that were the reverse of those associated with cingulotomies.
As painful stimulation was applied to his left arm
, he reported that he was receiving a “clearly unpleasant” feeling from somewhere between his fingertips and his shoulders.
But he was unable to give a more precise location.
And when asked to characterize the nature
of the pain—hot, cold, or pinprick-like—he could not choose any of these.
He was distressed by the pain, but he didn’t know where it was on his body or how to describe it.
If we were to make an analogy to reading a book, the somatosensory cortex seems responsible for understanding the type of story we are reading (thriller, detective novel, sci-fi) and its content, whereas the dACC is more responsible for one’s emotional reaction to the narrative.
We know that these reactions are separable since we can remember our emotional reactions to books long after we forget the plotlines.

The Anterior Cingulate Cortex and Attachment

The dACC and the ACC more generally are also critically important to attachment-related behavior for both mothers and their young.
As we discussed earlier, mammalian young produce distress vocalizations when they are separated from their mothers or care-givers.
Reptiles, from which mammals evolved, do not produce distress vocalizations, or any vocalizations at all—they are mute.
And it’s a good thing because most reptilian parents would likely eat their young if the young reptiles drew attention to themselves.
The fact that mammalian crying serves as a cue for maternal support, rather than as a dinner bell, is a major evolutionary difference.

Neuroscientist Paul MacLean experimented with the effects of
lesioning
(that is, surgically disconnecting) different parts of the
medial frontal cortex
(which includes the ACC) on the distress vocalizations produced by squirrel monkeys when socially isolated.
The only region whose removal consistently eliminated distress calls was the dACC.
When other regions were lesioned while leaving the dACC intact, the distress calls continued.
MacLean noted that all of the monkeys continued to produce other kinds of vocalizations (“yaps,” “cackles,” and “shrieks”) postoperatively, regardless of which region he lesioned, indicating that these regions were not, per se, involved in the physical production of vocal sounds.

If removing the dACC eliminates distress calls, then one would think the electrical stimulation of the same region would generate them.
And this is exactly what happens.
When the dACC is stimulated in rhesus monkeys
, they elicit the
köö
, a call that is specific to social isolation.
In contrast, a warning call—a different kind of call—was elicited by stimulating other brain regions, but never by stimulating the dACC.

From these studies, we can begin to see the potential consequences to the infant’s ability to form and maintain attachment bonds if the dACC is damaged.
Isolated infants who don’t cry are at a much greater risk of being left behind.
And if the mother’s dACC is damaged, she is less able to receive the infant’s call on her end of the attachment walkie-talkie.
To examine the effects of parents’ dACC lesions on infants,
female rats in one study were treated in one of three ways
prior to giving birth.
Some received cingulate lesions, some received noncingulate lesions (that is, lesions to other brain regions), and a third group received no surgery at all.
The focus of the study was to examine how these lesions would affect the survival rates of the new pups born to these different types of mothers.
The experimenters increased the harshness of the environmental conditions by adding heat and wind elements in certain parts of the cage to simulate conditions that might exist outside the lab.

Nearly every one of the pups of the mother rats who had not undergone surgery survived the first week.
When the heat blasts hit their part of the cage, these mothers would corral all their pups over to an unaffected part of the cage.
Moms with noncingulate lesions did almost as well, although some of their pups did not make it.
But the consequences of the cingulate lesions were devastating.
In this condition, only 20 percent of the pups survived the first two days after birth.
These moms would not nurse their young, they built poor nests, they did not collect their pups when they strayed from the nest, and they dealt poorly with protecting their young from heat and wind.
These mothers were unresponsive to the needs
of their young.
The difference between life and death for the pups was literally determined by whether their mothers had an intact cingulate or not.
As an aside, if you find yourself distressed by this story, it probably means your own dACC is intact.

Cyberball

As suggestive as this animal data is, it does not tell us whether social pain is linked to the experience of physical pain in humans.
Around 2001, Naomi Eisenberger and I decided to try to answer this question.
We had just received a grant to study the role of the ACC in social cognition.
We knew we wanted to study social rejection, but we had not come up with an ideal way to study it while someone was lying inside an MRI scanner.

As is often the case in science, random events intervened and changed the course of our research.
We were at a conference in Australia that neither one of us really belonged at.
It was there that we heard Kip Williams talk about a new experimental paradigm he had created for studying social rejection.
It was entirely Internet based, yet it was highly effective at producing feelings of social rejection, so it translated well into the fMRI scanning environment.

Kip Williams’s paradigm was called
Cyberball
, and it was a variant of a behavioral paradigm he had already been using successfully.
In his first studies, a subject would show up and be told to wait for a few minutes.
In the waiting room, two other people were already sitting, waiting for the same study.
In reality, the other two people were what psychologists call
confederates
, which means they were pretending to be subjects and were actually working for the experimenter.
One of the confederates would appear to “spontaneously” discover a tennis ball and would throw it to the other confederate, who would then toss it to the actual participant.
Over the next minute or two, the three of them would toss the ball around in a triangle.
However, at a prearranged time, the two confederates
would stop throwing the ball to the real participant, and instead they would throw it back and forth to each other.

Imagine you are the person who has been left out of the game that you were all playing so nicely.
On the one hand, you might think, “Who cares?
It’s not a real game and I don’t know these people—they are complete strangers.”
That would be a very rational response, and undoubtedly some participants try to rationalize their sudden exclusion in this way.
Yet, based on the measures Williams took, it was clear that these outcasts were in fact feeling social pain.
It hurts to be left out, even in such a trivial way.
After running a few of these waiting room studies, Williams created
Cyberball
, which replicated this scenario digitally.
When playing
Cyberball
, the participant believes she is throwing the digital “ball” around with two other real people connected over the Internet.
But in actuality she is playing only with preprogrammed avatars (see
Figure 3.3
) that stop throwing her the ball after a short while.